Delay initiators

ABSTRACT

In delay initiators used to initiate detonating explosives, a delay composition which comprises a metal salt of trinitrotoluene.

United States Patent Donald N. Thatcher Newark, Del.

Aug. 19, 1968 Jan. 19, 1971 E. 1. duPont de Nemours and Company Wilmington, Del.

a corporation of Delaware Inventor Appl. No, Filed Patented Assignee DELAY INITIATORS 13 Claims, 2 Drawing Figs.

U.S. Cl 102/28, 102/29, 149/23, 149/24,l49/27,149/28,149/105 Int. Cl C06c 1/00, C06h 9/04 [50] Field ofSearch 102/28, 29;

Primary Examiner-Leland A. Sebastian Att0rney-lohn F. Schmutz ABSTRACT: In delay initiators used to initiate detonating explosives, a delay composition which comprises a metal salt of trinitrotoluene.

PATENTED JAN 1 9 I971 FIG. I

INVENTOR DONALD N. THATCHER DELAY INITIATORS BACKGROUND OF THE INVENTION Delay blasting caps or initiators generally comprise, in addition to the usual base charge, primer charge, and ignition charge, a delay charge interposed between the ignition and primer charges. These initiators are designed to detonate at a predetermined period of time after energy is applied to the ignition system. This delay period is determined during manufacture by the quantity and burning characteristics of the delay charge and. by its confinement. Delay blasting caps are used to fire a number of explosive charges in planned sequence. Delay firing offers the advantages of greater safety, greater convenience, and more reliable timing, in that complete rounds may be fired in a desired sequence from a single application of electric current to electric delay initiators, and the need'to return to the blasting site between shots is thereby eliminated.

It has been proposed that delay blasting caps be prepared having a delay element comprising a loose charge positioned between a conventional ignition assembly, including an ignition composition, and the priming charge in the tubular initiator shell. Generally, however, to obtain the degree of reliability needed for commercial applications, the delay charge must be pressed and confined in a heavy-walled tubular metal carrier. The use of such a delay element necessitates, of course, the trouble and expense of loading and compressing the delay charge in the bore of the tubular carrier, cutting the tubular carrier into predetermined lengths, and inserting these delay elements into shell during assembly of the initiators. Particularly for use on mechanized assembly lines, it would be highly desirable to provide a particulate delay composition that could be charged into the initiator shell by machinery similar to that used to load the base and primer charges. Heretofore, however, no available composition has had an unconfined burning rate uniform enough for use as the delay element in a delay initiator. It would also be desirable to combine the delay charge and the ignition charge into a single delay-ignition charge, thus eliminating one charging operation.

SUMMARY OF THE INVENTION The present invention provides delay initiators that are easy and inexpensive to assemble and that are reliable in performance. The present invention provides delay initiators of the type comprising a tubular shell containing at least one detonating explosive charge and means for initiating the detonating explosive charge a predetermined period after application of energy to the delay initiator, the improvement wherein said means comprises a metal salt of trinitrotoluene (hereinafter TNT), the cationic portion of which salt is selected from alkali metals, alkaline earth metals, lead, silver, copper, iron, and aluminum. It is preferred that a burning rate modifier, especially dibasic lead phosphite, be mixed with the metal salt of TNT.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is further illustrated in the accompanying drawings, which show two preferred embodiments of the invention.

FIG. 1 is a cross-sectional view of an electric delay initiator in accordance with this invention. FIG. 2 is a cross-sectional view of a fuse actuated initiator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Metals that can he used to form the cationic portion of the metal salts used in the instant invention include alkali metals such as sodium, potassium, and lithium; alkaline earth metals such a barium, calcium, and magnesium; and heavy metals such as lead, silver, copper, aluminum, and iron. The monoand di-substituted alkali metals salts of TNT and alkaline earth metal salts of TNT can be prepared by the reaction of TNT with a hydroxide or an alkoxide of the metal. The heavy metal salts can be formed by a metathesis reaction between an alkali metal salt of TNT and a water-soluble heavy metal salt such as a nitrate, a chloride, a sulfate, or an acetate. Preferably, for availability and ease of handling, the metal TNT salt used is a sodium, a potassium, or a lead salt of TNT. Sodium TNT, for example, can be easily prepared by bringing into contact a solutionof TNT in methanol and an equimolar quantity of sodium methoxide as a 25 percent aqueous solution, evaporating the solution to dryness, and isolating the dark red product.

Various mixtures of the metal TNT salts described herein can be used to regulate more closely the delay periods of the initiators. The metal TNT salts can be used in accordance with the instant invention as a delay charge in conjunction with a separate ignition chaRge of the type usually used for delay initiators. However, the metal TNT salts described herein have been found to be effective in both an ignition and a delay charge. Therefore, it is preferred that they be used alone, i.e., without a separate ignition charge, thereby avoiding an additional step in the assembly of the initiator.

Although a pure metal salt of TNT can be used as the ignition-delay charge in accordance with this invention, a burning rate modifier is preferably mixed ,with the TNT salt. The use of at least one burning rate modifier such as dibasic lead phosphite or an oxidizer is preferred for economy, ease in handling, and control of burning characteristics. Such oxidizers can include, for example, chlorates such as potassium chlorate and sodium chlorate, perchlorates such as potassium perchlorate, potassium permanganate, peroxides such as bariurn peroxide, nitrates such as ammonium nitrate and sodium nitrate, and mixtures of the foregoing. The burning rates of the charges can be controlled by the quantity and type of such additives. A particularly preferred additive is dibasic lead phosphite, which corresponds to the formula 2Pb0 PbHPO H20. In compositions having a burning rate modifier with the TNT salt, the metal salt of TNT generally comprises about 5 to 50 percent by weight of the composition, the remainder comprising at least one burning rate modifier. A particularly preferred ignition-delay composition comprises about 20 to 30 percent of a sodium salt of TNT and the remainder dibasic lead phosphite.

The accompanying drawings illustrate two particular embodiments of the present invention.

FIG. 1 is an electric blasting cap comprising a tubular shell 1 having an integral closed end. Adjacent to the end is loaded a base charge 2. Such a base charge can consist of any explosive conventionally used for such purposes, such as pentaerythritol tetranitrate, cyclotrimethyl-enetrinitramine, picric acid, trinitrotoluene, tetryl, or mixtures thereof. Above the base charge 2 is a primer charge 3 which can be any of the primary explosives (highly sensitive to flame or shock) conventionally used, for example, lead azide or mercury fulminate. The delay-ignition composition 4 of this invention is loosely loaded above and in propagating relationship with the primer charge 3. The open end of the shell 1 is sealed by an ignition assembly comprising a plug 5 of a dielectric composition, preferably rubber, which mounts insulated leg wires 6 that extend below the lower portion of the plug into the delay-ignition charge 4 and are joined by a high-resistance bridgewire 7. The plug 5 is retained in the shell 1 by circumferential crimps 8.

The initiator shown in FIG. 2 is substantially the same as that of FIG. 1 except that the electric ignition assembly comprising elements 5, 6, and 7 is replaced by fuse 9 which can be a deflagrating fuse such as safety fuse, a low energy detonating cord, or a mild detonating fuse.

The action of both types of initiators is similar. In the electric delay initiator, electric current applied to the bridgewire heats to to the ignition temperature of the composition, e.g. about 200 C. for the monosodium salt of TNT, within a short period of time depending on the metal ion associated with TNT. The ignition-delay charge ignites, burns slowly for the time of the desired delay period, and then causes the primer charge to detonate and initiate the high explosive base charge. In the nonelectric delay initiator, the electrical ignition assembly. \lZ, leg wires, plug, and bridgewire, is replaced by a fuse. e.g.. safety fuse. low energy detonating cord, or mild detonating fuse. in this embodiment, the delay-ignition charge is ignited by either the spit and sparks from burning safety fuse or the detonation of the small load of high explosive core in low energy detonating cord. The delay period is determined by the burning rate of the particular metal TNT salt, by the quantity of it present, by the proportion of burning rate modifier used with it, and, in an electric initiator, the length of time required to bring the delay charge to its ignition temperature, which length of time, however, is usually not a significant part of the total delay time.

Delay detonators of the present invention possess improved static-electricity-resistant properties compared with known detonators. The noted improvement in static-electricity-resistance is due to the novel delay-ignition charge, which is very insensitive to needle point-to-plate static discharges when compared with other ignition powders, e,g., boron-red lead compositions.

The novel delay-ignition charge possesses excellent storage stability even in heated magazines. For example, a sample of a 30/70 mixture of sodium salt of TNT and dibasic lead phosphitc, stored in cardboard boxes at 100 F. for a period of 2 years, did not deteriorate. Detonators prepared from this stored powder sample functioned normally.

In the following examples, parts and percentages are by weight unless otherwise indicated.

EXAMPLE I A solution of 227 parts of trinitrotoluene in 3200 parts of methanol is treated with 22l parts of a 25 percent solution os sodium methoxide in methanol. The solution turns a dark red color. The methanol solution is evaporated to dryness, and the remaining solid material is ground to pass a 42-mesh screen. The powdered material is slurried three times with 900 parts of benzene to remove any traces of unreacted trinitrotoluene and then is air dried. The monosodium salt oftrinitrotoluene is obtained in 94--98 percent yield (235 parts).

In a similar manner, if the above example is repeated using subsequently identified as the corresponding metal salts, i.e., the silver, copper, lead, and barium salts, of TNT. The compounds are air dried, crushed, and passed through an 80-mesh screen.

In like manner, the aluminum and iron salts of TNT are prepared by repeating the above procedure substituting aluminum and iron salts for silver, copper, lead, and barium salts.

EXAMPLES 3-12 Electric balasting caps are assembled according to the design illustrated in FIG. 1. Into a commercial bronze shell, 1% inches long having an outer diameter of about 0.272 inch and an average inner diameter of about 0.260 inch, is loaded about 5 grains of pentaerythritol tetranitrate PETN), pressed at about 225-25O lbs. with a pointed pin. Immediately above this base charge, about 2.2 grains of lead azide is loaded and pressed at about 200 lbs. with a blunt pin. Desired amounts of different metal salts of TNT prepared as described in Exam ples l and 2 are loaded above the primer charges of lead azide and are left loose or unpressed. A conventional rubber plug ignition assembly having a 0.0015 inch diameter bridgewire (resistance 0.81 i 0.25 ohm) soldered to the leg wires is inserted on top of the loose charge such that the bridgewire is embedded in the loose charge. The leg wires fixed in the rubber plug are about 8 feet long and are 23-gage iron insulated by a plastic composition. After the cap is loaded and the plug inserted, three peripheral crimps are made in the shell wall to seal the plug.

The caps described above are fired, singly, by a current of 5 amperes, and the firing time of each, i.e., the time between application of a S-ampere electric current to the bridgewire and the detonation of the base charge, is recorded in milliseconds. In Table l are listed the firing times of caps containing different amounts of different metal salts of TNT.

In Examples 8, 9, and 10, the powdered metal salt of TNT is intimately mixed with a burning rate modifier, in finely divided form, in the proportions indicated in Table l, and this mixture is loaded into the cap shell on top of the primer charge of lead azide.

TABLE 1 Amt. of Firing time, milliscc. charge, No. of Salt of TNT grains caps fired Average Range 4. 0 5 15. 4 14. 546. 5 4. 0 5 33.1 I 31.4-35.1 4. 0 5 3.6 3. 2-4. 1 3. 0 10 8. 24 7. 8-9. 0 3.0 10 13. (l 12.8-14.1 3. 0 10 3. 5 3. 24. 1 6. 0 5 16. 5 14. 8-18. 3 6. 0 6 15. 0 13. (l-17.6 5. 0 5 16. 8 16.3-17.5 3. 5 5 30. 0 26. 8-31. 6

potassium hydroxide, potassium cyanide, or barium hydroxide in methanol solution in place of sodium methoxide. the corresponding potassium or barium salt of trinitrotoluene is obtained.

EXAMPLE 2 17 parts AgNO in 250 parts water 12 parts OIl(NO3)g in 250 parts water 16.5 parts Pb(NO )O in 250 parts water 24 parts BaOl -2H O in 250 parts water.

The resulting precipitates are filtered, washed with water, and

EXAMPLES l3l7 Mixtures of the sodium salt of TNT and dibasic lead phosphite are prepared by mechanically mixing the finely divided compounds in a blender, agglomerating the powder with a 50/50 mixture of trichloroethane and a liquid polyfunctional mercaptan as a binder, (ThiokoV LP-2), passing the material through a 28-mesh sieve, and drying it in a hot oven (about F.) for about 24 hours. Such mixtures are ready for use in delay blasting caps of the present invention, or they can be stored for extended periods of time without deterioration or loss of sensitivity to ignition.

Electric blasting caps are assembled according to the design illustrated in FIG. 1. The shell is bronze, 1 3/16 inches long with an outer diameter of about 0.272 inch and an average inner diameter of about 0.260 inch. Into this shell is loaded about 5 grains of pentaerythritol tetranitrate pressed at 225- 250 lbs. with a pointed pin. Immediately above this base charge, about 3 grains of lead azide is loaded and pressed at about 200 lbs. with a blunt pin. A desired quantity of a mixture composed of about 30 parts by weight of sodium salt of TNT and about 70 parts by weight of dibasic lead phosphite, prepared as described above, is loaded as the ignition-delay charge above the primer charge of lead azide and is left loose or unpressed. A conventional rubber plug ignition assembly, in which a 0.00156 inch diameter platinum-tungsten amples 13-17, except that the bronze shell is 2% inches long, the ignition-delay charge is potassium salt of TNT, the ignition-delay charge is pressed at about 200 lb. with a flat-end pin and may be charged and pressed in more than one increment, and the electric ignition assembly is replaced by a short, uniform length of low energy detonating cord having a core load of l grain of PETN per foot.

These caps are fired singly, and the firing time of each, i.e., the time between initiation of the fuse and the detonation of bridgewire (resistance 1.10 i 0.20 ohm) is welded to the leg the base charge, is recorded in seconds. The burning time of wires which are separated to provide a %-inCh span and which project one-eighth inch from the base of the rubber plug, is inserted on top of the loose charge. The leg wires held by the rubber plug are approximately 8 feet long and are 23-gage the fuse is negligible with respect to the total firing time and is essentially thesarne foral lthe caps. in Table 3 are listed the firing times of capscontaining different quantities of potassi- 5 um salt of TNT.

TABLE 3 Quantity of ignition delay Firing time, seconds charge, No. of

grains caps Average Range Remarks Example 18 5 10 2.3 2.24-2.49 19 5 3.7 3. -4. 28 Pressed lincrement. 20 10 5 4.7 4.49-5. 18 Pressed2inc1'ements. 21 15 5 5.2 4.88-5.29 Pressediiincrements.

iron insulated by a plastic composition. After the cap is loaded and the plug inserted, three peripheral crimps are made in the shell wall to seal the plug.

For testing, five caps, all containing the same quantity of ignition-delay charge, assembled as described above, are connected in electrical series by joining the leg wires together and are fired by the electrical discharge from a conventional blasting machine. The firing time, i.e., the time from the discharge of the blasting machine until the detonation of the slowest cap,

is recorded in milliseconds. Four such series of five caps each are tested. In like manner, caps containing a different weight of igniti0n-delay charge are tested to show that longer or shorter firing times may be obtained by changing the quantity of ignition-delay charge. In Table 2 are listed the average firing time of each set of four series of five caps and the variation, i.e., the difference in firing times between the fastest and the slowest series in each set.

TABLE 2 Quantity 0 lgnitlon- Firing time, millisec.

delay charge, Average Variation grains Example:

EXAMPLES 18-2l F use-actuated blasting caps. of the design illustrated in FIG. 2, are assembled according to the procedure described in Ex- EXAMPLES 22-26 Electric blasting caps are assembled as in Examples 13-17, containing an ignition-delay charge comprising 6.5 grains of a mixture of sodium salt of TNT and dibasic lead phosphite. Different proportions of sodium salt of TNT and dibasic lead phosphite are used, as shown in Table 4, which lists the firing times of these caps.

Other burning rate modifiers, potassium chlorate, barium peroxide, or potassium permanganate are added to the mixture of sodium salt of TNT and dibasic lead phosphite in the ignition-delay compositions prepared as described in Examples l3-l7. Delay electric blasting caps assembled as described in Examples Iii-17 and containing 5.5 grains of the delay-ignition mixtures shown in Table 5 are fired singly with a blasting machine.

TAB LE 5 Firing time, millisec.

Nor

Ignition-delay mixture caps Average Variation Example:

27 10/45/45 Na'INT/KClO /DLP 1 10 10. 4 5.1

28. 10/45/45 Na'INT/KMnOdDLP 10 45. 4 13. 5

29 20/40/40 NaTNIIBaO /DLP 0 24.1 6.2

I DLP is dibasic lead phosphite. 2 6.5 grains 0! charge used.

EXAMPLES 30-37 The examples of Table 6 show the effect of various periods of storage on the firing times of delay detonators assembled as described in Examples l3l7 and containing 5.5 grains of 30/70 sodium salt of TNT/dibasic lead phosphite mixture. All caps are tired singly in 80 F. water with a blasting machine.

TABLE 6 Length of No. of Firing time, miliiseo. storage, caps Example months Storage conditions tested Average Variation 15 8.8 3.0 1 Atmospheric 8.4 4.8 1 100 F., 85% EH 5 8. 9 3. 4 7 Atmospheric 5 9,3 2. 5 7 100 F., 85% RH 5 14. 5 2.1 160F 5 20.4 7.1 16 Atmospheric... 4 10.3 2.0 24 do 5 11.8 8.1

l 85% RH environment by a saturated solution of (N H4) 2804 in a closed container in 100 F. oven.

2. A delay initiator of claim 1 wherein the means further comprises a burning rate modifier admixed with metal salt of trinitrotoluene,

3. A delay initiator of claim 2 wherein the trinitrotoluene metal salt comprises about from 5 to 50 percent by weight of the mixture of trinitrotoluene metal salt and burning rate modifier.

4. A delay initiator of Claim 3 wherein the modifier comprises dibasic lead phosphite.

5. A delay initiator of claim 1 wherein the trinitrotoluene is sodium trinitrotoluene.

6. A delay initiator of claim 1 wherein the trinitrotoluene is potassium trinitrotoluene.

7. A delay initiator of claim 1 wherein the trinitrotoluene is copper trinitrotoluene.

8. A delay initiator of claim 1 wherein the trinitrotoluene is silver trinitrotoluene.

9. A delay initiator of claim 1 wherein the trinitrotoluene is lead trinitrotoluene.

10. A delay initiator of claim 1 wherein the trinitrotoluene is barium trinitrotoluene.

11. A delay initiator of claim 1 wherein the trinitrotoluene is iron trinitrotoluene.

12. A delay initiator of claim 1 wherein the trinitrotoluene is aluminum trinitrotoluene.

13. in a delay initiator of the type comprising a tubular shell containing at least one detonating explosive charge and means for initiating the detonating explosive charge a predetermined period after application of energy to the delay initiator, the improvement wherein the means comprises a mixture of dibasic lead phosphite and from about 20 to 30 percent sodium trinitrotoluene.

burning rate metal salt of metal salt of metal salt of metal salt of metal salt of metal salt of metal salt of metal salt of 

1. In delay initiators of the type comprising a tubular shell containing at least one detonating explosive charge and means for initiating the detonating explosive charge a predetermined period after application of energy to the delay initiator, the improvement wherein said means comprises metal salt of trinitrotoluene, the cationic portion of which salt is selected from alkali metals, alkaline earth metals, lead, silver, copper, iron, and aluminum.
 2. A delay initiator of claim 1 wherein the means further comprises a burning rate modifier admixed with metal salt of trinitrotoluene.
 3. A delay initiator of claim 2 wherein the trinitrotoluene metal salt comprises about from 5 to 50 percent by weight of the miXture of trinitrotoluene metal salt and burning rate modifier.
 4. A delay initiator of Claim 3 wherein the burning rate modifier comprises dibasic lead phosphite.
 5. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is sodium trinitrotoluene.
 6. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is potassium trinitrotoluene.
 7. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is copper trinitrotoluene.
 8. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is silver trinitrotoluene.
 9. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is lead trinitrotoluene.
 10. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is barium trinitrotoluene.
 11. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is iron trinitrotoluene.
 12. A delay initiator of claim 1 wherein the metal salt of trinitrotoluene is aluminum trinitrotoluene.
 13. In a delay initiator of the type comprising a tubular shell containing at least one detonating explosive charge and means for initiating the detonating explosive charge a predetermined period after application of energy to the delay initiator, the improvement wherein the means comprises a mixture of dibasic lead phosphite and from about 20 to 30 percent sodium trinitrotoluene. 